Volatile Fatty Acids Recovery In A Reactive Primary Clarifier: A Pilot Case Study

Although the aim of primary clarifiers remains to remove particles, the removal of settleable solids affects downstream processes that rely on readily biodegradable oxygen demand (rbCOD) in proportion to nutrient removal demands. However, through some process modification the primary clarifier can be looked at as a physico-biochemical reactor able to accomplish: removal of settleable solids; increase rbCOD concentration in the primary effluent. Pilot-scale experiments were conducted at the 12 m³ water resource recovery facility of Université Laval to determine the effect of different factors on the fermentation process in a primary clarifier. The results showed that providing a sludge retention time larger than one day and a low recirculation flow rate from the bottom of the clarifier of about 15% of the influent flow rate are crucial factors for increased rbCOD concentration. They can lead to a VFAs yield up to 90 mgCH3COOHequivalent/gVSS, along with a 70% solids removal efficiency.